Label-free optical biosensor based on a dual-core microstructured polymer optical fiber

A design for high-sensitivity and label-free optical biosensor based on the principle of wavelength-selective resonant coupling between the cores of a dual-core microstructured polymer optical fiber (MPOF) is demonstrated. An immobilized antigen sensing biolayer on the walls of the holes in a water-filled microstructured core provides the ability to selectively capture antibody biomolecules. The change of the thickness of antibody biolayer can be detected based on the shift of the resonant wavelength, which is achieved between a water-filled microstructured core and a small core with a small air hole in the center through selectively directional resonant-coupling. Accordingly, the transmission spectra of the output port will present a notch at the resonant wavelength, which is very sensitively dependent on the thickness of the biolayer. Numerical simulations demonstrate that the proposed biosensor can get a sensitivity of up to 5.6 nm/nm. In addition, the sensor resolutions of the biolayer thickness as high as 0.012–0.015 nm are presented in the whole 600–840 nm region.